1. Field of the Invention
The present invention relates generally to a steering wheel used in an indoor facility for driving practice, a reactive wheel of a game system and a steering wheel of a vehicle, and more particularly to a steer-by-wire system, which employs a brake using magneto-rheological fluid as an actuator to provide a driver with smooth feeling, and to escape improper and potentially dangerous acceleration of the steering wheel by the active actuator when driver""s hands are released from steering wheel abruptly.
2. Description of the Prior Art
As well known to those skilled in the art, a driver is able to sense information on vehicle conditions and road surface conditions through a mechanical connection between a steering wheel and wheels of the vehicle. However, since a steer-by-wire system does not have any mechanical connection, an additional control is required to transmit suitable steering reaction force to the driver.
FIG. 1 shows a general structure of a steer-by-wire system using an active actuator of the prior art.
Referring to FIG. 1, in the steer-by-wire system of the prior art, there is no mechanical connection between a steering operator unit 700 and a steering actuator unit 710. When the steering operator unit 700 receives a steering input from a steering wheel 600, a motor of the steering actuator unit 710 turn the vehicle""s wheels 660 accordingly.
In other words, the steering system has a first steering column which is connected to the steering wheel 600 and is rotated by the same, and a second steering column which is installed at a distance from the first steering wheel and rotatable in situ. A motor 610 for providing steering reaction force to the driver via the steering wheel 600 is coupled with the first steering column via a gear 630. A motor 620 for steering the wheels 660 is engaged into the second steering column via a gear 630.
Also, an angle sensor 640 for detecting a rotation angle of the steering wheel 600 and a torque sensor for detecting torque applied to the steering wheel 600 are provided at one end of the first steering column. A controller 650 controls the motor 620 in response to signals applied from the steering wheel angle sensor 640 so as to regulate a rotation angle of the vehicle wheels 660. Also, the controller 650 controls the wheel steering motor 610 so that the steering wheel can be manipulated with a feeling similar to that in the mechanical steering system.
In the steer-by-wire system of the prior art configured as above, the steering wheel 600 is required to serve as a conventional steering wheel for changing the direction of the travel of a vehicle according to a steering input of the driver, and at the same time to make the driver feel a suitable amount of steering force. Therefore, in addition to the above steering wheel 600, the steering system needs a rotation angle sensor for measuring an angle inputted by the driver and transmitting the same to the controller, and a steering wheel actuator for transmitting steering reaction force to the driver. Here, the steering wheel actuator is a very important component for influencing the controllability and stability of the steering wheel 600, and employs a motor.
However, when a system with low impedance such as the steering wheel 600 of the steer-by-wire system is force-feedback controlled by using an active actuator such as the motor, the steering wheel 600 can be accelerated by the motor or the actuator at the moment that the steering input is removed. Then, the stability of the system cannot be ensured. Therefore, an active actuator such as the motor is not suitable for the steering wheel 600 of the steering system, where stability is important. Also, in using an active actuator such as a motor, an oscillatory torque is transmitted to the steering wheel 600. Then, the driver feels vibration from the steering wheel that causes the driver to feel uncomfortable.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a steer-by-wire system using a semi-active actuator, in which a suitable amount of steering reaction force is supplied to a steering wheel by using a magneto-rheological brake as the semi-active actuator, by which stability can be promoted even if a driver input is removed, and a driver can feel smoothness in steering.
It is another object of the invention to provide a steer-by-wire system using a semi-active actuator which supplies steering reaction force to a steering wheel in response to driving conditions without a mechanical connection with wheels of a vehicle, and thus can be applied to the virtual reality system industry and the game industry.
In order to accomplish the above objects, the present invention provides a steer-by-wire system using a semi-active actuator, in which a wheel steering motor operates vehicle wheels when a steering wheel is rotated, the system comprising: a steering operator unit having a steering column with one end vertically connected to the center of the steering wheel, a torsion spring means connected between the other end of the steering column and a vehicle body via jigs mounted to both ends thereof, a magneto-rheological brake for providing steering reaction force according to the amount of current, a rotation angle sensor coupled with one end of the steering column for detecting rotation of the steering wheel, and a torque sensor coupled with one end of the steering column for detecting steering torque; a current regulator for controlling resistance force against rotation of the magneto-rheological brake; and a controller for controlling the current regulator according to torque data from the torque sensor, and controlling the wheel steering motor 110 according to rotational displacement data from the rotation angle sensor.
It is preferred that the magneto-rheological brake has a rotor fixed to the outer periphery of the steering column, a plurality of cores spaced apart from the rotor by a predetermined interval and wound with coils, and a housing spaced apart from the rotor by a predetermined interval for receiving the rotor and the plurality of cores, wherein the rotor, the plurality of cores and the housing define a space for containing a magneto-rheological fluid.
It is also preferred that the housing is fixed to the vehicle body to support rotation of the steering wheel, and the torsion spring means has a double structure of springs connected in parallel, in which one of the springs has diameter and spiral direction different from those of the other.
Also, it is preferred that the jigs are a pair shaped as a column, one of the jigs being centrally fixed to the steering wheel, and the other one of the jigs being fixed to the vehicle body.
In order to accomplish the above objects, the present invention further provides a steer-by-wire system using a semi-active actuator, in which a wheel steering motor operates vehicle wheels when a steering wheel is rotated, the system comprising: a steering operator unit having a first steering column vertically connected to the center of the steering wheel, a second steering column connected to the first steering column, a first torsion spring means connected between the first steering column and the second steering column via first jigs mounted to both ends thereof, a second torsion spring means connected between the second steering column and a vehicle body via second jigs mounted to both ends thereof, a first magneto-rheological brake for comparing torque by the first torsion spring means with the reference steering torque and providing resistance force to compensate for an error, a second magneto-rheological brake mounted to the second steering column for regulating torque by the first torsion spring means, a first rotation angle sensor coupled with one end of the first steering column for detecting angle displacement of the steering wheel, a second rotation angle sensor coupled with one end of the second steering column for detecting angle displacement of the second steering column, and a torque sensor coupled with one end of the first steering column for detecting steering torque; a current regulating unit having a first current regulator for controlling resistance force against rotation of the first magneto-rheological brake, and a second current regulator for controlling resistance force against rotation of the second magneto-rheological brake; and a controller for receiving data of the torque sensor 40, the first rotation angle sensor and the second rotation angle sensor to control the amount of current of the first current regulator and the second regulator and to control the wheel steering motor.
It is preferred that the first magneto-rheological brake has a rotor fixed to the outer periphery of the first steering column, a plurality of cores spaced apart from the rotor by a predetermined interval and wound with coils, and a housing spaced apart from the rotor by a predetermined interval for receiving the rotor and the plurality of cores, the rotor, the plurality of cores and the housing defining a space for containing a magneto-rheological fluid; and the second magneto-rheological brake has a rotor fixed to the outer periphery of the second steering column, a plurality of cores spaced apart from the rotor by a predetermined interval and wound with coils, and a housing spaced apart from the rotor by a predetermined interval for receiving the rotor and the plurality of cores, the rotor, the plurality of cores and the housing defining a space for containing a magneto-rheological fluid.
It is also preferred that the housing is fixed to the vehicle body to support rotation of the steering wheel, and the first torsion spring means has a double structure of springs connected in parallel, in which one of the springs has a diameter and a spiral direction different from those of the other.
Also, it is preferred that the second torsion spring means has a double structure of springs connected in parallel, in which one of the springs has a diameter and a spiral direction different from those of the other, and the second torsion spring means has stiffness lower than that of the first torsion spring means
Preferably, the first jigs are a pair shaped as columns, in which one of the first jigs is centrally fixed to the steering wheel, the other one of the first jigs is centrally fixed to the vehicle body.
Preferably also, the second jigs are a pair shaped as columns, in which one of the second jigs is centrally fixed to the steering wheel, the other one of the second jigs is centrally fixed to the vehicle body.